Package qt5-default is not available, but is referred to by another package.

The package "qt5-default" is not available in the current package repositories. However, it is referred to by another package that depends on it. You can try the following steps to resolve this issue:

1. Update your package repositories by running the command:

   sudo apt update

2. Install the necessary packages by running the command:

   sudo apt install build-essential

3. Install the Qt development libraries by running the command:

   sudo apt install qt5-qmake qtbase5-dev

These steps should help resolve the issue and install the necessary packages for Qt development. If you still encounter any issues, please provide more details about your system and any error messages you are receiving.